//: Playground - noun: a place where people can play

import Foundation

// Constraining the Element to NSObject makes sure that NSSortDescriptors can be used for comparison.
extension Collection where Iterator.Element: NSObject {
    func sorted(using descriptors: [NSSortDescriptor]) -> [Iterator.Element] {
        return self.sorted { (element1, element2) in
            for descrptor in descriptors {
                let compareResult = descrptor.compare(element1, to: element2)
                switch compareResult {
                case .orderedSame: continue
                case .orderedAscending: return true
                case .orderedDescending: return false
                }
            }
            return false
        }
    }
}

// Can be sorted with extended Collection sorted(using:) function.
class Thing: NSObject {
    let id: Int
    let name: String
    init(id: Int, name: String) {
        self.id = id
        self.name = name
        super.init()
    }

    override var description: String {
        return "\(id): " + self.name
    }
}

// Can't be sorted with extended Collection sorted(using:) function.
class Foo: Hashable {
    let id: Int
    let name: String
    init(id: Int, name: String) {
        self.id = id
        self.name = name
    }

    var hashValue: Int {
        return id
    }
}
func ==(lhs: Foo, rhs: Foo) -> Bool {
    return lhs.id == rhs.id
}


var mySet: Set<Thing> = [Thing(id: 10, name: "Ten"), Thing(id: 1, name: "One"), Thing(id: 1, name: "AOne"), Thing(id: 2, name: "Two"), Thing(id: 4, name: "Four"), Thing(id: 3, name: "Three")]

// compiler won't offer sorted(using: [NSSortDescriptor]) since this Array type isn't NSObject.
var fooSet: Set<Foo> = [Foo(id: 10, name: "ten"), Foo(id: 1, name: "one")]

let sorts = [NSSortDescriptor(key: "id", ascending: true), NSSortDescriptor(key: "name", ascending: true)]
var sorted = mySet.sorted(using: sorts)

print(sorted)
// [1: AOne, 1: One, 2: Two, 3: Three, 4: Four, 10: Ten]